The present invention relates in general to semiconductor devices and, more particularly, to integrated circuits having components formed on a low capacitance region of a semiconductor die.
Semiconductor technology continues to scale transistors to have smaller dimensions in order to provide increased functionality and a higher frequency capability. For example, wireless communication devices often use integrated circuits that include high-density digital signal processing functions on the same die as analog circuits operating at frequencies in excess of five gigahertz.
However, some integrated circuit components, such as passive devices, are not readily scalable. These devices have relatively high parasitic substrate capacitances, which often limits the overall frequency capability of an integrated circuit. For example, inductors are not easily reduced in size without reducing their quality factor or inductance to an unacceptable level, and bonding pads are not scalable because of the need to attach wire bonds to the bonding pads.
A variety of techniques have been tried to reduce the parasitic capacitances of passive integrated circuit components. One such technique is to form the components over a low permittivity material. However, current low permittivity materials are limited to film thicknesses that are too thin to produce a substantial reduction in parasitic capacitance. Another approach is to form the components over a thick dielectric film in which are formed air gaps or voids that reduce the overall permittivity of the dielectric film. Previously, voids were formed using thermally grown dielectric films to form the trench, and deposited films to seal them. However, voids made with such films introduce substantial stress in a semiconductor substrate, which degrades the performance and reliability of the integrated circuit. Also, these voids are not optimized for reducing capacitance due to the relatively high dielectric constant of the films used to form them. Furthermore, the voids are filled with these films during the sealing process producing a void with increased dielectric constant. Other schemes reduce the stress by producing fewer voids or voids with only a limited volume, which has a correspondingly limited effect on parasitic capacitance. Moreover, in order to avoid contaminating the transistors or reducing the die yield or reliability, complex and costly schemes are required to enable the integration of the low permittivity structures with active devices such as transistors.
Hence, there is a need for a low capacitance structure and method of making an integrated circuit that maintains a low cost while reducing die stress and avoiding the introduction of contaminants into the integrated circuit.